The invention relates to a method of growing monocrystals from a highly pure poly-crystalline material melt.
Such a method is known in principle, for example, from D. T. J. Hurle: Handbook of Crystal Growth 2a Basic Techniques, North Holland (1994), page 102 ff.
In a crucible consisting of quartz, an amount of silicon is molten and heated to maintain the silicon in a molten state. The crucible is disposed on a graphite containment. The melt is heated by heating rods transmitting heat by radiation to the graphite and from the graphite to the quartz crucible. From the quartz crucible, heat is transferred to the melt by heat conduction. The single crystal is drawn from the melt in the usual way.
This method however has a serious disadvantage in that the crucible needs to be hotter than the melt. The excess temperature of the crucible is greater the larger the diameter of the single crystal and, consequently, of the melt bath is. With increasing diameter of the melt bath, the heat flow through the quartz crucible must be increased so that also the temperature gradient providing for the increased heat flow from the quartz crucible to the melt is increased. As a result, the crucible becomes soft and, furthermore, a reaction occurs between the crucible and the melt whereby oxygen and crucible material are transferred to the melt thereby contaminating the melt.
It is the object of the present invention to provide a method of drawings single crystals from a melt wherein, during the melting of the crystal material and the heating of the melt, the melt remains in a highly pure state.